More work thrown at HscMain.
MkIface.writeIfaceFile doesn't check GhcMode anymore. All it does is what the name say: write an interface to disk. I've refactored HscMain so the logic is easier to manage. That means we can avoid running the simplifier when typechecking (: And best of all, HscMain doesn't use GhcMode at all, anymore! The new HscMain intro looks like this: It's the task of the compilation proper to compile Haskell, hs-boot and core files to either byte-code, hard-code (C, asm, Java, ect) or to nothing at all (the module is still parsed and type-checked. This feature is mostly used by IDE's and the likes). Compilation can happen in either 'one-shot', 'batch', 'nothing', or 'interactive' mode. 'One-shot' mode targets hard-code, 'batch' mode targets hard-code, 'nothing' mode targets nothing and 'interactive' mode targets byte-code. The modes are kept separate because of their different types and meanings. In 'one-shot' mode, we're only compiling a single file and can therefore discard the new ModIface and ModDetails. This is also the reason it only targets hard-code; compiling to byte-code or nothing doesn't make sense when we discard the result. 'Batch' mode is like 'one-shot' except that we keep the resulting ModIface and ModDetails. 'Batch' mode doesn't target byte-code since that require us to return the newly compiled byte-code. 'Nothing' mode has exactly the same type as 'batch' mode but they're still kept separate. This is because compiling to nothing is fairly special: We don't output any interface files, we don't run the simplifier and we don't generate any code. 'Interactive' mode is similar to 'batch' mode except that we return the compiled byte-code together with the ModIface and ModDetails.